Multiplex communications – Fault recovery
Reexamination Certificate
1998-06-11
2002-05-07
Chin, Wellington (Department: 2664)
Multiplex communications
Fault recovery
C370S535000
Reexamination Certificate
active
06385165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally Synchronous Optical Networks (SONET) and more specifically to a SONET add-drop multiplexer.
2. Description of the Related Art
A ring-topology interconnection network is formed of a plurality of add-drop multiplexers connected to an optical fiber ring. Each add-drop multiplexer includes a working system for multiplexing low-speed uplink signals to a high speed uplink signal and demultiplexing a high-speed downlink signal to a plurality of low-speed downlink signals. A spare system is provided to backup the working system. However, due to the duplicated structure, one half of the transfer capacity of the add-drop multiplexer is not utilized. Therefore, there is a need to increase the transport capacity of the add-drop multiplexer of duplicated configuration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an add-drop multiplexer of duplicated configuration that can double its transport capacity.
According to a first aspect of the present invention, there is provided an add-drop multiplexer of duplicated configuration, comprising a first low-speed working system, a first low-speed spare system, a second low-speed working system, a first high-speed system, a second high-speed system, and means for establishing a two-way connection between the first low-speed working system and one of the first and second high-speed systems and for establishing a one-way connection from one of the first low-speed spare system and the second low-speed working system to the second high-speed system and a one-way connection from the second high-speed system to the first low-speed spare system and the second low-speed working system.
In a preferred embodiment, the add-drop multiplexer further includes a second low-speed spare system, the arrangement being such that a one-way connection is established from one of the first low-speed spare system and the second low-speed working and spare systems to the second high-speed system and a one-way connection is established from the second high-speed system to the first low-speed spare system and the second low-speed working and spare systems. In a further preferred embodiment, the add-drop multiplexer further includes means for preventing the first low-speed spare system from recognizing a faulty condition of the second low-speed working and spare systems.
According to a second aspect, the present invention provides an add-drop multiplexer of duplicated configuration, comprising first and second cross-connect systems, at least one pair of first and second protection switches, the first protection switch being connected to an input port of the first cross-connect system, at least one third protection switch, at least one selector for selectively connecting one of the second, and third protection switches to an input port of the second cross-connect system, an output port of the second cross-connect system being connected to the second and third protection switches through a node, and a pair of fifth and sixth protection switches connected to output ports of the first and second cross-connect systems. A first multiplexer/demultiplexer is provided for multiplexing signals from the fifth protection switch into an uplink high-speed signal and demultiplexing a downlink high-speed signal into a plurality of signals and supplying the demultiplexed signals to input ports of the first and second cross-connect systems. A second multiplexer/demultiplexer multiplexes signals from the sixth protection switch into an uplink high-speed signal and demultiplexes a downlink high-speed signal into a plurality of signals and supplies the demultiplexed signals to input ports of the first and second cross-connect systems. In a preferred embodiment, the add-drop multiplexer further includes at least one fourth protection switch, the selector being arranged such that it selectively connects one of the second, third and fourth protection switches to an input port of the second cross-connect system, wherein the output port on the first side of the second cross-connect system is connected to the second, third and fourth protection switches through a node.
Preferably, the add-drop multiplexer further comprises a bit sequence generator for producing a predetermined bit sequence and a selector connected between the node and the second protection switch for selectively connecting one of the node and die bit sequence generator to the second protection switch.
REFERENCES:
patent: 5978353 (1999-11-01), Iwahori et al.
Chin Wellington
NEC Corporation
Pham Brenda
Scully Scott Murphy & Presser
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